Exothermic and endothermic reactions

[705801855]

Can someone explain how we know which way the reaction will shift for both endothermic and exothermic reactions if heat is added?

[Elise Wu 1G]

When heat is added to a chemical system, the formation of higher enthalpy molecules will be favored. Therefore, in an endothermic reaction, where products have a higher enthalpy than reactants, product formation is favored since the reaction requires heat to form product. In an exothermic reaction, reactants will be favored since they have a greater enthalpy than products.

[Sophia Spallone 1A]

To start, exothermic reactions release heat, while endothermic reactions require heat. If a reaction uses heat to form a product (endothermic), and you add more heat to the system, you will be able to form more product. Thus, adding heat to an endothermic reaction will cause it to shift to the right. Conversely, if a reaction gives off heat when forming a product, and you add more heat to the system, you will be able to form more reactant. Thus, adding heat to an exothermic reaction will cause it to shift to the left. In both of the cases of endothermic and exothermic reactions, when you add heat, the additional heat is used.
Additionally, another way to think about it is that exothermic reactions have products with a lower enthalpy than the reactants. Endothermic reactions have products with higher enthalpy than the reactants. When you heat a system, the reaction favors the side with a higher enthalpy, so, for an exothermic reaction, more reactants will be produced. When you cool a system, the reaction favors the side with a lower enthalpy, so, for an exothermic reaction, more products are produced.

[Luka Gogorishvili 1K]

In a nutshell:
Putting heat into a system favors whatever has greater enthalpy in that system;
Cooling a system favors whatever has less enthalpy in that system.

As Dr. Lavelle stated in his lecture, endothermic reactions take in energy - thus, products will have greater enthalpy in this reaction. Exothermic reactions release energy, so reactants will have greater enthalpy. If you cool an exothermic reaction, you will get more product as it has less enthalpy and if you cool an endothermic reaction, you will get more reactant for the same reason. Heating an exothermic reaction will get you more reactants and heating an endothermic reaction will get you more products.

[Sulaimanshah Syed 3E]

We know that in exothermic reactions, heat is being released making the reaction favor reactants. In endothermic reactions, heat is being used thus the formation of products will be favored.

[BB Richardson 2E]

Can someone explain how we know which way the reaction will shift for both endothermic and exothermic reactions if heat is added?

If the forward reaction or reaction going from reactants to products has a negative value, it is considered exothermic. Because it is exothermic, it tells you that products are favored in cooler environments. If you then decrease the temperature, then more products should form. The reverse is also true.

[Ashley Chu 3C]

If the reaction requires heat to form product this means that it is endothermic and if heat is added to the reaction, the reaction will shift right as the additional heat is used to product more product. If the reaction gives off heat to form product that means that the reaction is exothermic and if heat is added to the reaction, the reaction will shift to the left as the additional heat is used to form more reactants.

[Julia_Wong_1H]

Enthalpy is the internal energy of a system plus the product of pressure and volume. Thus, when heat is added to the system, the production of higher enthalpy molecules will be favored. Products are favored in an endothermic reaction where products have a higher enthalpy than reactants (heat is used to form the product). Reactants are favored in an exothermic reaction since they have a greater enthalpy than products (heat is released from the formation of products).

[Paul Torres 2I]

In an exothermic reaction, the reaction will shift to the left if you add heat. This is because an exothermic reaction releases heat, and in order to regain equilibrium, the reaction will favor the reactants and shift to the left. In an endothermic reaction, heat is required to form the products; therefore, if heat is added, the reaction will favor the products and will shift to the right.

[Levon_Avedian_2H]

Which type of reaction is more efficient during chemical reactions and why?

[Fiorella Garcia 3D]

In an endothermic reaction heat is required thus the products are favored. On the other hand, in an exothermic reaction heat is released thus favoring the reactants.

[Justin Shafa 2E]

How do we know if the reaction releases heat or doesn't?

[Nadia Svejda 3L 14B]

If heat is added to a system, it will shift to whichever side has a higher enthalpy. In other words, it will shift towards the things that require heat. In endothermic reactions, the products require heat to form, and they have higher enthalpy than the reactions’ products. Thus, if you add heat, the reaction will shift to the right, towards the heat-dependent products. In exothermic reactions, the reaction must give off heat to form, and they have lower enthalpy than the reactions’ products. Thus, if you add heat, the system will compensate by shifting to the left, towards the products (which by definition have a higher enthalpy in exothermic reactions).

[Anthony Lau-Xiao 1E]

I think one way you will know if the reaction releases heat or not is if you are given a balanced chemical equation and given the enthalpies for each of the bonds for the molecules. On the reactants side it will be positive since it requires energy to break and on the products side it will be negative since it releases heat. You would then calculate the overall net change in enthalpy for the reaction. If you get a positive value then it is an endothermic reaction and requires heat. But if you get a negative value then it is an exothermic reaction and releases heat.

[Tatum Pearlman 2D]

Heating always favors whatever has a higher enthalpy in a reaction. In an endothermic reaction, the enthalpy of the products is higher than the reactants, so products will be favored and therefore the forward reaction will be favored. In an exothermic reaction, the enthalpy of the reactants is higher than the products, so reactants will be favored and the reverse reaction will be favored.

[Nishanth Vemuri 2L]

Exothermic means that delta H for the reaction is negative, so heat is released from the system. Endothermic means that delta H is positive, so heat is added into the system. If we are adding heat into an exothermic reaction, in which the reactants have a higher enthalpy than the products (since products - reactants = negative), we are moving the equilibrium towards the left, so more reactants are formed. In an endothermic reaction, products have a higher enthalpy than the reactants (products - reactants = positive), so adding heat will favor the products.

[Mallika Mathew]

When you heat a system whatever has higher enthalpy will be favored. In an exothermic reaction, heat is liberated so the products have lower enthalpy and therefore the backward reaction (reactant formation) will be favored. Conversely, in an endothermic reaction heat is required to form products so the products have higher enthalpy and therefore the forward reaction (product formation) will be favored.

[EmiD 2H]

To clarify, a positive delta H value is endothermic and a negative delta H value is exothermic?

[Daniel Hong 3F]

Yes a positive delta H value is endothermic and a negative delta H value is exothermic.

[Brandon_Leong_2J]

When heat is added, the reaction will favor the direction in which more heat is required (the side which has a higher enthalpy). So for instance if the forward reaction is exothermic, adding heat will favor the reverse reaction (bc the reverse reaction is endothermic, which therefore means it has a higher enthalpy).

[Levon_Avedian_2H]

Why do exothermic reactions release heat and why do endothermic reactions save heat? What is the significance and what causes it?

[Sydney_Hoang_Dis1B]

I don't understand the spontaneity and how it relates to Gibbs Free Equation. Can someone help me by explaining this?

[yesmal1J]

If ΔG is negative, the reaction is spontaneous as written.
If ΔG is positive, the reaction as written is nonspontaneous, but the reverse reaction is spontaneous.
If ΔG is zero, the reaction is at equilibrium at the given temperature.

[Jeanelle Ocampo 2L]

For endothermic reactions, the reaction shifts to the right. More products are formed.
For exothermic reactions, the reaction shifts to the left. More reactants are formed.